In an apparatus incorporating a backup battery such as an uninterruptible power supply (UPS), it is important to detect the life of the battery from the viewpoint of maintenance and inspection. In general, the deterioration of life of a nickel-hydride battery is mainly caused by corrosion of a hydrogen storage alloy of a negative electrode, but is often influenced by such factors as the use temperature, the number-of-discharges, the magnitude of load power in discharge, and the like. In this way, the factors for determining the life of the battery are diversified, and hence, it is not easy to accurately determine the life of the battery in use.
Conventionally, it is proposed to use an increase in the internal resistance at the end of life of the battery and a voltage change in discharge as parameters in order to determine the life of a nickel-hydride battery. For example, there are disclosed an apparatus which performs deterioration determination by calculating a gradient of discharge voltage values based on the distribution of the discharge voltage values corresponding to plural discharge current values (for example, patent document 1), and an apparatus which performs deterioration determination by relatively comparing values of internal resistance and battery voltage which are measured during discharge with their initial values (for example, patent document 2). In these life determination methods, attention is directed to a correlation of the internal resistance of the battery with the resultant voltage change and life of the nickel-hydride battery, and hence, these methods are effective in that it is possible to estimate the life of the battery to some degrees in a short period time.
On the other hand, there is proposed a method in which an expected life value of a battery is calculated from a discharge load power value and in which the difference between the expected life value and a life reduction amount calculated as a linear function with the number-of-discharges as a variable is used as a remaining life value to determine the life of the battery (for example, patent document 3). This method makes it possible to use a highly precise expected life value by suitably correcting the value without forcibly making the battery discharge, and hence, is effective for a lead-acid battery, and the like.
Patent document 1: Japanese Laid-Open Patent Publication No. 8-138759
Patent document 2: Japanese Laid-Open Patent Publication No. 2000-215923
Patent document 3: Japanese Laid-Open Patent Publication No. 2000-243459